Seasonal changes in the vertical distribution of dust in the lower troposphere

Measurements of solar radiation at two different elevations in Phoenix, Arizona, yield a mean transmittance difference between the two levels (Δ elevation = 464 meters) of 0.012 for the summer period May through August and 0.066 for the winter period November through February. Theoretical calculations of the transmittance of the atmosphere yield very similar values for these periods, if we assume that most of the atmospheric dust in winter is confined to this surface layer and that atmospheric dust in the summer is more evenly distributed to about 3000 meters. A mechanism is proposed to explain this seasonal variation in the vertical distribution of surface-generated dust, and local meteorological data are presented to support its validity.